The present invention relates generally to process chambers and, more particularly, to a getter system for purifying the confinement volume in process chambers.
Thin layers of metallic or ceramic materials deposited by, e.g., physical vapor deposition (PVD), which is also referred to as "sputtering," are used in a variety of applications. For example, in the semiconductor industry, a number of layers are deposited by PVD and then selectively removed in the fabrication of integrated circuits. In the compact disc and digital versatile disc (DVD) industries, the reflective layer of aluminum is deposited by PVD.
The processes used to deposit such thin layers require the use of high purity gases. In particular, in the fabrication of semiconductors, impurities in the process gases may result in microflaws in the electronic devices. In general, the smaller the size of the device, the greater the effect such microflaws have on the operability of the device. In light of the continuing trend to reduce the average size of electronic devices, the use of increasingly pure process gases is required to obtain an acceptable yield percentage.
A common practice in the semiconductor industry for purifying gases upstream of a process chamber, e.g., a PVD process chamber, is the use of getter materials in combination with conventional pumps. Even when the purity of the inlet gases is controlled, however, impurities may be introduced in the chamber as the result of the degassing of the materials forming the walls or other parts of the chamber. For example, contamination is a significant problem in the deposition of aluminum and titanium nitride layers. In the sputtering process typically used to deposit such layers, the flat surface of a target, which consists of the material to be deposited, is eroded by the impact of ions of heavy atoms, e.g., Ar+ ions, that have be accelerated by a suitable electric field. The particles removed from the surface of the target are deposited in the form of thin layers onto the substrate of semiconductor material, which faces the target and is generally arranged so as to be parallel to the surface of the target. During the sputtering process, the gases within the target, e.g., gases mechanically incorporated into the structure of the material during production, are discharged and result in a high concentration of impurities in the confinement volume. The most common impurities are H.sub.2 O, H.sub.2, CO, CO.sub.2, and CH.sub.4, and the concentration of these impurities may range, depending upon the specific features of each deposition process, from about 1 ppm to about 100 ppm.
International Publication Nos. WO 96/13620, WO 96/17171, and WO 97/17542, European Publication No. 0 693 626, and U.S. Pat. No. 5,778,682 to Ouellet disclose in situ getter pump systems for purifying gases arranged inside process chambers, e.g., PVD chambers. These in situ getter pump systems are disposed within the process chambers at locations outside of the confinement volume. One of the main advantages of such an in situ getter pump system is that it substantially reduces the pump down time required for the chamber to reach acceptable vacuum and impurity levels after the chamber has been opened, e.g., for maintenance operations.
The in situ getter pump systems disclosed in the above-listed references do not fully solve the problem of impurities within the confinement volume during PVD operations because this volume is defined by screens that prevent the target material from being deposited onto undesired portions of the chamber, e.g., feedthroughs, openings for connecting the chamber to gas lines, etc. These screens significantly reduce the gas conductance between the confinement volume and the remaining volume of the chamber and thereby create two different gaseous atmospheres within the processing chamber. As a result of this reduced gas conductance, the sorption of impurities in the confinement volume by the in situ getter pump systems disclosed in the above-listed references is negligible. Thus, the problem of effectively purifying the gaseous atmosphere within the confinement volume during PVD operations so that contamination of the deposited layers is avoided remains unsolved.
In view of the foregoing, there is a need for a mechanism that effectively purifies the gaseous atmosphere within the confinement volume of a process chamber, e.g., a PVD chamber, such that contamination of the deposited layers is avoided.